When it comes to looks go for what you like!
As you asked for a comparison of the WE to the KJW M4 then the KJW is Much More Reliable BY Far!
I know a bunch of guys over at Gas Guns Info (where I am a Super User/Lower Level Mod) and they spend money on their guns Everytime out just to keep it running. Mags cost $20 more up to 2 X as much as the KJW M4.
But if you have money to keep spending on a gun to keep it running - Even more frequently if you plan to upgrade it - and having to keep a back up AEG on hand as you can't really be sure if the gun will keep running all day, much less than all weekend like at a Big Op.
Again - ONLY Speaking of reliability between WE PDW and KJW M4,,,